C12 : The Solar System

Section 1 : The Solar System P. 337 Fig 1 Sun contains ______% of the mass of the solar system. → great gravity → holds the planets and other objects in the solar system. 1 Astronomical unit (Au) – the average distance between Earth and the Sun. ~ 150 million km.

Q: Any other body beyond Pluto in the solar system? A: Astronomers are studying the movements of Pluto to det. whether the gravity of an object farther out is affecting Pluto.

Formation of the Solar System and Planets

A cloud of gas and dust in space was disturbed by supernova. Explosion caused waves which squeezed the cloud. Squeezing increased the gravity pull and and the cloud of gas and dust come together to form solar nebula.

The cloud began to spin faster as it collapsed. The cloud grew hotter and denser in the center. The edge gets thinner and cooler. As the disk got thinner, ptles began to stick together and form clumps. Some clumps got bigger forming planets or moons.

Near the center of the cloud, only rocky material could stand the great heat. Example: Earth. Icy matter settled in the outer regions of the disk. The center eventually got so hot that it became a star, the Sun.

Lighter elements are scarcer in the planets near the Sun than in planets farther out in the solar system. Planets closer to the Sun travel _______ than planets farther away from the Sun.

Section 2 : The Inner Planets Mercury Venus Earth Mars

Mercury Venus Earth Mars

Mercury Many craters → like Earth’s Moon Cliffs ~ 3 km Weak magnetic field → iron core No atmosphere. Why? Temps: 425°C → - 170°C

Closest to Sun 2nd smallest planet in solar system No moons

Venus Earth’s twin : size and mass very similar. Clouds (carbon dioxide) are very dense → very little sunlight enters. Heat is absorbed by CO2 in the atm →greenhouse effect 45°C → 475°C

Yellow color → clouds of H2SO4 Surface has craters, volcanoes No moons

Earth Q: How does Earth’s atm helps to protect us? A: It causes most meteors to burn up before they reach the surface. It also shields us from Sun’s intense radiation. Q: Why does the Earth appear to be blue? A: ocean color

Mars

Reddish yellow → iron oxide in soil. Polar ice caps → made of frozen CO2 & H2O Olympus Mons → largest volcano in the solar system.

Q: The two closest planets to Earth are Venus and Mars Q: The two closest planets to Earth are Venus and Mars. But when astronauts from Earth visit another planet, it will be Mars rather than Venus. Why? A: Venus has very high temps and atm press (dense clouds) → caused space probes to malfunction and conditions more hostile for humans.

Mar’s atm is much thinner than Earth’s → mostly CO2. Surface temp : - 125°C → 35°C 2 small moons – heavily cratered - Phobos - Deimos (farther away)

Section 3 : The Outer Planets

Jupiter

5th planet from Sun Atm : hydrogen and helium Largest planet in solar system Great Red Spot : giant storm about 25 000 km At least 61 moons

4 Large Moons of Jupiter Io : active volcanoes : red and orange → sulfurous compounds : atm – thin oxygen : closest to Jupiter

Europa : rocky interior : 100 km thick crust of ice : thin O2 atm : possible ocean as deep as 200 km under the ice

3. Ganymede : crust of ice ~ 500 km thick : rocky core : thin oxygen atm : largest moon (bigger than Mercury)

4. Callisto : crust of ice and rock a few hundred km thick : crust might surround a salty ocean : rocky core : thin CO2 atm

Saturn

Sixth planet 2nd largest in solar system Lowest density Thick atm : hydrogen & helium Complex ring system

Structure of Saturn

Saturn’s rings → ice and rock ptles At least 31 moons Largest moon : Titan Atm : Nitrogen; Argon; Methane

Uranus

7th planet ~ 21 moons Largest moon : Titania : craters & deep valleys

Gaseous planet Atm : hydrogen; helium; methane Bluish green → CH4

Neptune

8th planet Atm : similar to Uranus Bluish green → methane

At least 11 moons Largest moon : Triton Atm: nitrogen Gaseous planet

Pluto

Smallest planet in solar system Orbit round the Sun → 248 years Different from other outer planets: - thin atm - solid, icy rock surface 1 moon : Charon (half the size of pluto)

Section 4: Other objects in the Solar System Comets Meteoroids Asteroids

Comets

Halley’s Comet Composed of dust & rock ptles (like large dirty snowball) mixed with frozen water, CH4 & NH3

Oort Cloud Billions of comets surround the solar system Located beyond the orbit of Pluto Gravity of the Sun and nearby stars gravities interact with the comets in the cloud Either escape from the solar system or get captured into smaller orbits

Structure of Comet Approaches Sun → frozen ice, CH4, NH3 vaporize → release dust and bits of rock Coma: the gases and released dust form a bright cloud Nucleus: solid part of comet (unmelted frozen ice) Solar wind pushes on the gases and dust in the coma → form tails

Meteoroids When comets vaporize and break up → small pieces from the comet’s nucleus spread in the original orbit of the comet → These pieces of dust and rock is called meteoroids

Meteoroids which enter Earth are small → burn up in Earth’s atm → meteor Meteor Showers : more meteors enter the atm of Earth. Occurs when Earth crosses the orbital path of a comet. Meteorite : big meteoroid not burning up in the atm and hits the Earth. They are debris from asteroid collisions or broken up comets.

Asteroids Rock similar to the planet Located in asteroid belt – between orbits of Mars and Jupiter Tiny ptles to rocks 940 km in diameter